In recent years, efforts have been made to shorten the fast forwarding and rewinding times (FF/REW of a video tape device, and to shorten the image reproduction time during fast forward and rewinding modes.
The present invention relates to capstan control which makes it possible to transfer a tape at high speeds and to picture signal processing which makes it possible to reproduce the tape images during high speed tape running operations.
The speed controlling operation of the capstan which is accompanied through the higher speed of the FF/REW will be described hereinafter.
FIG. 1 is a block diagram showing the construction of the conventional rotary head type magnetic record reproducing apparatus such as servo mechanism of a VTR. In FIG. 1, a cylinder control apparatus is composed of a cylinder motor 1 having a rotary head (not shown), a first frequency generator 14 for detecting the rotation speed of the cylinder motor 1, a phase detector 15 for detecting the rotation phase of the cylinder motor 1, a cylinder speed comparing circuit 20 for detecting the errors with respect to the reference period of the output signal of the first frequency generator 14, a reference signal generator 24, a cylinder phase comparing circuit 21 for detecting the phase errors between the rotation phase signals to be obtained by the phase detector 15 and the reproducing reference signals to be obtained from the reference signal generator 24, a first adder 22 for mixing the phase error output of the cylinder phase comparing circuit 21 and the speed error output of the cylinder speed comparing circuit 20, and a cylinder driving circuit 23 which is controlled by the output of the first adder 22 so as to drive the cylinder motor 1.
A capstan control apparatus is composed of a capstan 3 which comes into pressure contact against the pinch roller 4 with a magnetic tape 7 being grasped therebetween to transfer the magnetic tape 7, a capstan motor 2 for driving the capstan 3, a second frequency generator 16 for detecting the rotation speed of the capstan motor 2, a control head 8 for recording and reproducing the control signals on the lower end of the magnetic tape 7, a capstan speed comparing circuit 25' for detecting the error with respect to the reference period of the output signal of the second frequency generator 16, a tracking shifting circuit 29 to be triggered by the output signals of the reference signal generator 24, a capstan phase comparing circuit 26 for detecting the phase errors between the reproducing control signal to be obtained from the control head 8 and the output signal of the tracking shifting circuit 29, a second adder for mixing the phase error output of the capstan phase comparing circuit 26 with the speed error output of the capstan speed comparing circuit 25', and a capstan driving circuit 28 which is controlled by the output of the second adder 27 so as to drive the capstan motor 2.
A magnetic tape driving apparatus is composed of a center pulley 9 to be rotated and driven through a belting 10 by a capstan motor 2, a supply side reel 5 and a winding side reel 6 with the magnetic tape 7 being wound around them, a supply side reel gear 12 and a winding side reel gear 13 for driving the respective reels, an idler 11 for transferring to either the supply side reel gear 12 or the winding side reel gear 13 the rotation of the center pulley 9 in accordance with the running direction of the magnetic tape 7.
The normal reproduction operation of the VTR constructed hereinabove will be simply described with reference to the block diagram of FIG. 1 and the timing chart shown in the FIG. 2.
Reference character S1 of FIG. 2 is the output waveform of a reference signal generator 24 of FIG. 1. The signal is fed into the cylinder phase comparing circuit 21 and a tracking shifting circuit 29 as the reference signal at the reproduction time of the VTR. The trapezoidal wave signal S2 of FIG. 2 is of an internal waveform of the cylinder phase comparing circuit 21, is a phase reference signal of the cylinder motor 1 triggered by the rising edge reference signal of the S1 of FIG. 2, is sampled by the falling edge of the rotation phase signal to be obtained from the phase detector 15, namely, by the falling edge of the signal S3 of FIG. 2, is fed to the cylinder driving circuit 23 with the phase error signal (not shown) of the held cylinder motor 1 and the speed error signal to be obtained from the cylinder speed comparing circuit 20 being mixed by a first adder 22. Accordingly, the cylinder motor 1 is rotated in the phase synchronous relation with the reference signal S1 of FIG. 2. The signal S4 of FIG. 2 is of the output waveform of the tracking shifting circuit 29. The trapezoidal wave signal S5 of FIG. 2 is of an internal waveform of the capstan phase comparing circuit 26, is a phase reference signal of the capstan motor triggered by the falling edge of the output signal S4 of the tracking shifting circuit 29, is sampled by the rising edge of the reproducing control signal to be obtained from the control head 8, namely, by the rising edge of the S6 signal of FIG. 2, is fed into the capstan driving circuit 28 with the phase error signal (not shown) of the held cylinder motor 2 being mixed by the second adder 27 with the speed error signal to be obtained from the capstan speed comparing circuit 25'. The capstan motor 2 is rotated in the phase synchronous relation with the output signal of the tracking shifting circuit 29 of the S4 of FIG. 2 with the reference signal of the S1 of FIG. 2 being shifted in phase. The capstan motor 2 is rotated in the phase synchronous relation with the output signal of the tracking shifting circuit 29 with the reference signal S1 of FIG. 2 being shifted in phase. At the normal reproducing time of the VTR, the rotation head (not shown) mounted on the cylinder motor 1 and the reproduction control signal (FIG. 2, S6) are put into the phase synchronous relation, so that the rotation head is adapted to optimally follow the track recorded on the magnetic tape 7.
The rotation of the capstan motor 2 is transferred into the center pulley 9 through the belt 10, is transferred into the winding side reel gear 13 at the normal reproducing time by an idler 11 to clockwise rotate the winding side reel 6 for winding up the magnetic tape 7, retaining the proper tension. At the time of the reverse reproduction of the review reproduction, the idler 11 falls onto the left-hand side to counterclockwise rotate the supply side reel 5, and winds up the tape with the tension of the magnetic tape 7 being retained so that the magnetic head (not shown) may properly trace the track recorded on the magnetic tape 7.
In order to forward wind the magnetic tape 7 at high speeds (hereinafter referred to as FF mode) or to rewind (hereinafter referred to as REW mode) it, the pinch roller 4 of FIG. 1 is isolated from the capstan 3 and winds the magnetic tape 7 with the constant speed rotation of the capstan motor 2 at high speeds. In this case, the capstan phase comparing circuit 26 is made ineffective, the capstan motor 2 is controlled in speed with the capstan speed comparing circuit 25' only.
The block diagram showing the inner construction of the capstan speed comparing circuit 25' in the conventional VTR of FIG. 1 is shown in FIG. 3. In FIG. 3, it is composed of a first counter 31 for counting the clock pulses (which are represented as CLK in FIG. 3), a first register 30 for fetching the digital outputs, a first timing generator 34 for outputting the various types of timing pulses in synchronous relation with the above described clock pulses in accordance with the rotation detecting signal (which is represented as CAFG in FIG. 3) which changes in period in accordance with the rotation speed of the capstan motor 2, an AND gate circuit 35 for masking the above described clock pulses, and a first data register 33 for feeding the digital initial value with respect to the first counter 31.
The operation of the capstan speed comparing circuit 25' constructed hereinabove will be simply described with reference to block diagram of FIG. 3 and the timing chart of the major essential portions shown in FIG. 4. The reference character A of FIG. 4 is a clock pulse to be inputted from the terminal 50 of FIG. 3, is a basic unit of a clock signal of the first counter 31, namely, the reference speed, is also a synchronizing signal of the above described various types of timing pulses. The reference character B of FIG. 4 is a rotation detecting signal to be inputted from the terminal 51 of FIG. 3, is inputted into the first timing generator 34 so as to compose the clock gate pulses C of FIG. 4, the latch pulses D of FIG. 4, and the preset pulses of E of FIG. 4. The digital initial value accommodated in the first data register 33 is preset in the first counter 31 with the preset pulse E. Immediately after it, the clock pulse A cut off in the AND gate circuit 35 by the clock gate pulse C is fed into the first counter 31. The first counter 31 starts its counting operation. The analog data F shows the counting operation so as to fetch the digital values of the first counter 31 into the first register 30 by the latch pulse D to be generated by the arriving of the next rotation detecting signal B. The clock gate pulse C is adapted to stop the digital operation of the first counter 31 to retain the stable operation when the digital initial value is preset in the first counter 31 and when the digital value of the first counter 31 is fetched into the first register 30. The data F fetched into the first register 30 are converted from the digital into analog, and are outputted. In order to make the operation point in the steady condition constant, the digital initial value (which is assumed to be NPO) to be accommodated in the first data register 33 so that the digital value to be fetched into the first register 30 may become a given value (which is assumed to be NF) when the capstan motor 2 is rotating at a set speed. Assume that the reference period of the rotation detecting signal B of the capstan motor 2 is To and the frequency of the clock pulse A is fck, and the digital initial value NPO is obtained in the follow formula. EQU NP0=NF-fck-To (1)
In order to switch the set of the rotating member, the digital initial value NPO accommodated in the first data register 33 is changed or the rotation detecting signal B to be inputted into the timing generator 34 is divided in frequency to effect the inputting operation.
The problem in the above described construction is that the tape speed is changed in accordance with the tape winding diameter of the reel as the capstan motor 2 is controlled at speed in the capstan speed comparing circuit 25' only in the FF/REW mode for winding and rewinding the magnetic tape at high speeds. As the rotation speed of the capstan motor 2 is constant, the rotation speed of the winding side reel 6 in, for example, FF mode becomes constant. The more the tape is wound, the bigger the winding diameter becomes. The peripheral speed, namely, the tape speed increases, so that the speed of the tape trailing end become maximum. In order to prevent tape damage at the stop time of the tape trailing end, a certain limit value is provided in the maximum speed. It cannot be set in the tape speed beyond it, namely, the capstan speed. Therefore, there is a problem in that the FF/REW time cannot be shortened.
The image reproducing operation at the high speed time will be described hereinafter.
In order to effect the high speed running operation with the tape being fully loaded on the rotation cylinder in the conventional video tape recorder, the vertical and horizontal frequencies of the reproducing signal change by the running speed of the magnetic tape and the rotation speed of the cylinder. Therefore, up to a certain tape speed, the reproducing signal may be imaged on the picture face with the synchronizing signal being separated in the processing portion of the reproducing signal. Once it is beyond a certain speed, the synchronous separation cannot be effected. The vertical or horizontal flowing is caused on the picture face, so that normal images cannot be seen. Namely, in the conventional video tape recorder as shown in FIG. 1, the horizontal frequency of the reproducing signal changes when the rotary cylinder is rotated at almost the same speed as the normal reproducing operation at the high speed running operation of the magnetic tape 7. When the speed correction is effected so that the relative speed of the rotary cylinder 1 and the magnetic tape 7 may become the given frequency in the horizontal frequency as in the special reproducing operation at this time, the vertical frequency changes. If the reproducing signal is imaged as it is on the television image receiving machine, the vertical or the horizontal flowing is caused on the image, with a problem arising in that the reproducing operation cannot be effected on the normal picture face.
In the conventional video recorder, discriminating operation is effected as to which head output from each head output is larger in the fast forwarding reproduction and rewinding reproduction so as to switch the head. As the speed of the tape becomes faster, the head switching signal is generated from the head output. The optimum head output cannot be obtained due to the time delay required to actually switch the head.
FIG. 5 is a block diagram showing the construction from the head output of the conventional video tape recorder to the head switching operation. In the drawing, a rotary head L'101, a rotary head R'102, a rotary head L103, and a rotary head R104 are mounted in the symmetrical positions of the rotary, cylinder 105. The rotary head L'101 and the rotary head L103 are adjacent each other, and the R'102 and the head R104 are adjacent each other. The rotary head L'101 is connected with a head amplifier L'106. The rotary head R'102 is connected with a head amplifier R'107. The rotary head L103 is connected with a head amplifier L108. The rotary head R104 is connected with a head amplifier R109. A head amplifier L'106 and a head amplifier R'107 are connected with a head SW circuit 110. The head amplifier L108 and the head amplifier R109 are connected with a head SW circuit 111. The head SW circuits 110, 111 are connected with a head amplifier SW circuit 113 and an envelope comparing circuit 112, the output signals from the head SW circuits 110, 111 are switched in the head amplifier SW circuit 113 so as to output the amplified signals into a reproduction signal processing circuit 114.
In the waveform forming apparatus of a video tape recorder constructed hereinabove, the output signals from the head amplifier L'116 and the head amplifier R'117 are switched by a head SW circuit 110 in the reference reproducing mode so as to output them into the head amplifier SW circuit 113. The head amplifier SW circuit 113 amplifies the output signal from the head SW circuit 110 so as to output it into the reproducing signal processing circuit 114. In the long hour reproduction mode, the output signals from the head amplifier 108 and the head amplifier 109 are switched by the head SW circuit 111 and are outputted into the head amplifier SW circuit 113. The head amplifier SW 113 circuit amplifies the output signal from the head SW circuit 111, which is outputted into the reproduction signal processing circuit 114.
As the rotary head R'102 and the rotary head R104, and the rotary head L'101 and the rotary head L103 are mounted in adjacent relation, the signals from the head amplifier R'107 are outputted from the head SW circuit 110 when the rotary head R'102 and the rotary head R104 trace the magnetic tape, and the signal from the head amplifier R109 is outputted from the head SW circuit 111. The signals from the head amplifier L'106 are outputted from the head SW circuit 110 when the head L'101 and the head L103 trace the magnetic tape, the signals from the head amplifier L108 are outputted from the head SW circuit 111. In the special reproduction, the output signals from the head SW circuits 110, 111 are compared with by an envelop comparing circuit 112 so as to discriminate which head output is larger so as to feed the head output switching signal into the head amplifier SW circuit 113. In the head amplifier SW circuit 113, the signals from the head SW circuits 110, 111 are switched in accordance with the head output switching signal so as to feed them into the reproduction signal processing circuit 114 after the amplification thereof.
In such a conventional video tape recorder, the number of track crossings by the head into one vertically scanning operation increases when the magnetic tape has been caused to effect the high speed running operation, and the increase or decrease of the output from the head becomes intense. The frequency of the head output switching signal from the envelope comparing circuit becomes higher. Thus, the optimum head output cannot be obtained due to the time delay from the comparison of the respective head output amplitude to the actual head switching operation.